Relationship between work rate and oxygen uptake in mitochondrial myopathy during ramp-incremental exercise

We determined the response characteristics and functional correlates of the dynamic relationship between the rate (Δ) of oxygen consumption ( O2) and the applied power output (work rate = WR) during ramp-incremental exercise in patients with mitochondrial myopathy (MM). Fourteen patients (7 males, age 35.4 ± 10.8 years) with biopsy-proven MM and 10 sedentary controls (6 males, age 29.0 ± 7.8 years) took a ramp-incremental cycle ergometer test for the determination of the O2 on-exercise mean response time (MRT) and the gas exchange threshold (GET). The ΔO2/ΔWR slope was calculated up to GET (S1), above GET (S2) and over the entire linear portion of the response (S T). Knee muscle endurance was measured by isokinetic dynamometry. As expected, peak O2 and muscle performance were lower in patients than controls (P < 0.05). Patients had significantly lower ΔO2/ΔWR than controls, especially the S2 component (6.8 ± 1.5 vs 10.3 ± 0.6 mL·min-1·W-1, respectively; P < 0.001). There were significant relationships between ΔO2/ΔWR (S T) and muscle endurance, MRT-O2, GET and peak O2 in MM patients (P < 0.05). In fact, all patients with ΔO2/ΔWR below 8 mL·min-1·W-1 had severely reduced peak O2 values (<60% predicted). Moreover, patients with higher cardiopulmonary stresses during exercise (e.g., higher Δ ventilation/carbon dioxide output and Δ heart rate/ΔO2) had lower ΔO2/ΔWR (P < 0.05). In conclusion, a readily available, effort-independent index of aerobic dysfunction during dynamic exercise (ΔO2/ΔWR) is typically reduced in patients with MM, being related to increased functional impairment and higher cardiopulmonary stress.

A new proposal to guide velocity and inclination in the ramp protocol for the treadmill ergometer

OBJECTIVE: To suggest criteria to guide protocol prescription in ramp treadmill testing, according to sex and age, based on velocity, inclination, and max VO2 reached by the population studied. METHODS: Prospective study describing heart rate (HR), time, velocity, inclination, and VO2 estimated at maximum effort of 1840 individuals from 4 to 79 years old, who performed a treadmill test (TT) according to the ramp protocol. A paired Student t test was used to assess the difference between predicted and reached max VO2, calculated according to the formulas of the "American College of Sports Medicine". RESULTS: Submaximal HR was surpassed in 90.1% of the examinations, with a mean time of 10.0±2.0 minute. Initial and peak inclination velocity of the exercise and max VO2 were inversely proportional to age and were greater in male patients. Predicted Max VO2 was significantly lower than that reached in all patients, except for female children and adolescents (age < 20 years old). CONCLUSION: Use of velocity, inclination, and maximum VO2 actually reached, as a criterion in prescribing the ramp protocol may help in the performance of exercise in treadmill testing. The ramp protocol was well accepted in all age groups and sexes with exercise time within the programmed 8 to 12 minutes.

Heart Rate Variability Correlates to Functional Aerobic Impairment in Hemodialysis Patients

Background:Autonomic dysfunction (AD) is highly prevalent in hemodialysis (HD) patients and has been implicated in their increased risk of cardiovascular mortality.Objective:To correlate heart rate variability (HRV) during exercise treadmill test (ETT) with the values obtained when measuring functional aerobic impairment (FAI) in HD patients and controls.Methods:Cross-sectional study involving HD patients and a control group. Clinical examination, blood sampling, transthoracic echocardiogram, 24-hour Holter, and ETT were performed. A symptom-limited ramp treadmill protocol with active recovery was employed. Heart rate variability was evaluated in time domain at exercise and recovery periods.Results:Forty-one HD patients and 41 controls concluded the study. HD patients had higher FAI and lower HRV than controls (p<0.001 for both). A correlation was found between exercise HRV (SDNN) and FAI in both groups. This association was independent of age, sex, smoking, body mass index, diabetes, and clonidine or beta-blocker use, but not of hemoglobin levels.Conclusion:No association was found between FAI and HRV on 24-hour Holter or at the recovery period of ETT. Of note, exercise HRV was inversely correlated with FAI in HD patients and controls. (Arq Bras Cardiol. 2015; [online]. ahead print, PP.0-0)

Effects of aerobic exercise training on heart rate variability during wakefulness and sleep and cardiorespiratory responses of young and middle-aged healthy men

The purpose of the present study was to evaluate the effects of aerobic physical training (APT) on heart rate variability (HRV) and cardiorespiratory responses at peak condition and ventilatory anaerobic threshold. Ten young (Y: median = 21 years) and seven middle-aged (MA = 53 years) healthy sedentary men were studied. Dynamic exercise tests were performed on a cycloergometer using a continuous ramp protocol (12 to 20 W/min) until exhaustion. A dynamic 24-h electrocardiogram was analyzed by time (TD) (standard deviation of mean R-R intervals) and frequency domain (FD) methods. The power spectral components were expressed as absolute (a) and normalized units (nu) at low (LF) and high (HF) frequencies and as the LF/HF ratio. Control (C) condition: HRV in TD (Y: 108, MA: 96 ms; P<0.05) and FD - LFa, HFa - was significantly higher in young (1030; 2589 ms²/Hz) than in middle-aged men (357; 342 ms²/Hz) only during sleep (P<0.05); post-training effects: resting bradycardia (P<0.05) in the awake condition in both groups; VO2 increased for both groups at anaerobic threshold (P<0.05), and at peak condition only in young men; HRV in TD and FD (a and nu) was not significantly changed by training in either groups. The vagal predominance during sleep is reduced with aging. The resting bradycardia induced by short-term APT in both age groups suggests that this adaptation is much more related to intrinsic alterations in sinus node than in efferent vagal-sympathetic modulation. Furthermore, the greater alterations in VO2 than in HRV may be related to short-term APT.

Identification of anaerobic threshold using heart rate response during dynamic exercise

The objective of the present study was to characterize the heart rate (HR) patterns of healthy males using the autoregressive integrated moving average (ARIMA) model over a power range assumed to correspond to the anaerobic threshold (AT) during discontinuous dynamic exercise tests (DDET). Nine young (22.3 ± 1.57 years) and 9 middle-aged (MA) volunteers (43.2 ± 3.53 years) performed three DDET on a cycle ergometer. Protocol I: DDET in steps with progressive power increases of 10 W; protocol II: DDET using the same power values as protocol 1, but applied randomly; protocol III: continuous dynamic exercise protocol with ventilatory and metabolic measurements (10 W/min ramp power), for the measurement of ventilatory AT. HR was recorded and stored beat-to-beat during DDET, and analyzed using the ARIMA (protocols I and II). The DDET experiments showed that the median physical exercise workloads at which AT occurred were similar for protocols I and II, i.e., AT occurred between 75 W (116 bpm) and 85 W (116 bpm) for the young group and between 60 W (96 bpm) and 75 W (107 bpm) for group MA in protocols I and II, respectively; in two MA volunteers the ventilatory AT occurred at 90 W (108 bpm) and 95 W (111 bpm). This corresponded to the same power values of the positive trend in HR responses. The change in HR response using ARIMA models at submaximal dynamic exercise powers proved to be a promising approach for detecting AT in normal volunteers.

The decreased oxygen uptake during progressive exercise in ischemia-induced heart failure is due to reduced cardiac output rate

We tested the hypothesis that the inability to increase cardiac output during exercise would explain the decreased rate of oxygen uptake (VO2) in recent onset, ischemia-induced heart failure rats. Nine normal control rats and 6 rats with ischemic heart failure were studied. Myocardial infarction was induced by coronary ligation. VO2 was measured during a ramp protocol test on a treadmill using a metabolic mask. Cardiac output was measured with a flow probe placed around the ascending aorta. Left ventricular end-diastolic pressure was higher in ischemic heart failure rats compared with normal control rats (17 ± 0.4 vs 8 ± 0.8 mmHg, P = 0.0001). Resting cardiac index (CI) tended to be lower in ischemic heart failure rats (P = 0.07). Resting heart rate (HR) and stroke volume index (SVI) did not differ significantly between ischemic heart failure rats and normal control rats. Peak VO2 was lower in ischemic heart failure rats (73.72 ± 7.37 vs 109.02 ± 27.87 mL min-1 kg-1, P = 0.005). The VO2 and CI responses during exercise were significantly lower in ischemic heart failure rats than in normal control rats. The temporal response of SVI, but not of HR, was significantly lower in ischemic heart failure rats than in normal control rats. Peak CI, HR, and SVI were lower in ischemic heart failure rats. The reduction in VO2 response during incremental exercise in an ischemic model of heart failure is due to the decreased cardiac output response, largely caused by depressed stroke volume kinetics.

Moderate-term reproducibility of heart rate variability during rest and light to moderate exercise in children

Previous studies have demonstrated the high reproducibility of heart rate variability (HRV) measures in adults while little information exists concerning HRV reproducibility in children. Subsequently, the aim of the current study was to examine the moderate-term reproducibility of heart rate and frequency domain measures of HRV during rest and light to moderate exercise in children. Ten healthy children (6 males, 4 females) aged between 7 and 12 years of age volunteered for this study with HRV recordings obtained during supine rest and three treadmill walking exercise work rates (≤60% maximum heart rate), initially and then 8 weeks later. Differences (P < 0.05) between variables were examined using paired t-tests or Wilcoxon signed rank tests while reliability and reproducibility were examined by intraclass correlation coefficients (ICC), coefficients of variation (CV), and mean bias ratio and ratio limits of agreement (LOA). Heart rate and all measures of HRV at rest and exercise were unchanged after 8 weeks. Significant ICC were documented primarily during rest (0.72-0.85) while weaker relationships (-0.02-0.87) were evident during exercise. A large range of CV was identified during rest (6-33%) and exercise (3-128%) while the ratio LOA were variable and substantial (1.04-2.73). Despite similar HRV over an 8-week period, variable ICC and sizable CV and ratio LOA indicate moderate to poor reproducibility of HRV in children, particularly during light to moderate exercise. Studies examining HRV in children should include age- or maturation stage-matched control participants to address the age-related change in HRV and inadequate HRV reliability.

Reproducibility of heart rate variability parameters measured in healthy subjects at rest and after a postural change maneuver

Heart rate variability (HRV) provides important information about cardiac autonomic modulation. Since it is a noninvasive and inexpensive method, HRV has been used to evaluate several parameters of cardiovascular health. However, the internal reproducibility of this method has been challenged in some studies. Our aim was to determine the intra-individual reproducibility of HRV parameters in short-term recordings obtained in supine and orthostatic positions. Electrocardiographic (ECG) recordings were obtained from 30 healthy subjects (20-49 years, 14 men) using a digital apparatus (sampling ratio = 250 Hz). ECG was recorded for 10 min in the supine position and for 10 min in the orthostatic position. The procedure was repeated 2-3 h later. Time and frequency domain analyses were performed. Frequency domain included low (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-0.4 Hz) bands. Power spectral analysis was performed by the autoregressive method and model order was set at 16. Intra-subject agreement was assessed by linear regression analysis, test of difference in variances and limits of agreement. Most HRV measures (pNN50, RMSSD, LF, HF, and LF/HF ratio) were reproducible independent of body position. Better correlation indexes (r > 0.6) were obtained in the orthostatic position. Bland-Altman plots revealed that most values were inside the agreement limits, indicating concordance between measures. Only SDNN and NNv in the supine position were not reproducible. Our results showed reproducibility of HRV parameters when recorded in the same individual with a short time between two exams. The increased sympathetic activity occurring in the orthostatic position probably facilitates reproducibility of the HRV indexes.

Influence of exercise modality on agreement between gas exchange and heart rate variability thresholds

The main purpose of this study was to investigate the level of agreement between the gas exchange threshold (GET) and heart rate variability threshold (HRVT) during maximal cardiopulmonary exercise testing (CPET) using three different exercise modalities. A further aim was to establish whether there was a 1:1 relationship between the percentage heart rate reserve (%HRR) and percentage oxygen uptake reserve (%V˙O2R) at intensities corresponding to GET and HRVT. Sixteen apparently healthy men 17 to 28 years of age performed three maximal CPETs (cycling, walking, and running). Mean heart rate and V˙O2 at GET and HRVT were 16 bpm (P<0.001) and 5.2 mL·kg-1·min-1 (P=0.001) higher in running than cycling, but no significant differences were observed between running and walking, or cycling and walking (P>0.05). There was a strong relationship between GET and HRVT, with R2 ranging from 0.69 to 0.90. A 1:1 relationship between %HRR and %V˙O2R was not observed at GET and HRVT. The %HRR was higher during cycling (GET mean difference=7%; HRVT mean difference=11%; both P<0.001), walking (GET mean difference=13%; HRVT mean difference=13%; both P<0.001), or running (GET mean difference=11%; HRVT mean difference=10%; both P<0.001). Therefore, using HRVT to prescribe aerobic exercise intensity appears to be valid. However, to assume a 1:1 relationship between %HRR and %V˙O2R at HRVT would probably result in overestimation of the energy expenditure during the bout of exercise.

Considerations about the recommendations of the Commission on the Limits of the Continental Shelf on the Amazon fan

In 2004, Brazil submitted to the Commission on the Limits of the Continental Shelf (CLCS) a Submission for the outer limit of the Brazilian continental shelf for its extension beyond the limits of 200 nautical miles. In 2007, the CLCS presented its recommendations, however it did not recommend four areas proposed by Brazil, the Amazon Fan among them. The objective of this study is to present the main legal and technical aspects of the controversy about the Amazon Fan, in order to evaluate some alternatives for a future submission, new or revised.

Peaceful rise and the limits of Chinese exceptionalism

Throughout the last thirty years of opening to the world Beijing has stressed that its rise will be peaceful and that, from a strategic point of view, China is exceptional. There are many challenges facing Beijing's response to the US rebalancing to the Asia-Pacific, but we consider that the ones with greater impact are, in point of fact, of a domestic nature and constitute limits to Chinese exceptionalism.

Determination of reactivity rates of silicate particle-size fractions

The efficiency of sources used for soil acidity correction depends on reactivity rate (RR) and neutralization power (NP), indicated by effective calcium carbonate (ECC). Few studies establish relative efficiency of reactivity (RER) for silicate particle-size fractions, therefore, the RER applied for lime are used. This study aimed to evaluate the reactivity of silicate materials affected by particle size throughout incubation periods in comparison to lime, and to calculate the RER for silicate particle-size fractions. Six correction sources were evaluated: three slags from distinct origins, dolomitic and calcitic lime separated into four particle-size fractions (2, 0.84, 0.30 and <0.30-mm sieves), and wollastonite, as an additional treatment. The treatments were applied to three soils with different texture classes. The dose of neutralizing material (calcium and magnesium oxides) was applied at equal quantities, and the only variation was the particle-size material. After a 90-day incubation period, the RER was calculated for each particle-size fraction, as well as the RR and ECC of each source. The neutralization of soil acidity of the same particle-size fraction for different sources showed distinct solubility and a distinct reaction between silicates and lime. The RER for slag were higher than the limits established by Brazilian legislation, indicating that the method used for limes should not be used for the slags studied here.

Use efficiency of variable rate of nitrogen prescribed by optical sensor in corn

ABSTRACT The efficiency of nitrogen fertilizer in corn is usually low, negatively affecting plant nutrition, the economic return, and the environment. In this context, a variable rate of nitrogen, prescribed by crop sensors, has been proposed as an alternative to the uniform rate of nitrogen traditionally used by farmers. This study tested the hypothesis that variable rate of nitrogen, prescribed by optical sensor, increases the nitrogen use efficiency and grain yield as compared to uniform rate of nitrogen. The following treatments were evaluated: 0; 70; 140; and 210 kg ha-1 under uniform rate of nitrogen, and 140 kg ha -1 under variable rate of nitrogen. The nitrogen source was urea applied on the soil surface using a distributor equipped with the crop sensor. In this study, the grain yield ranged from 10.2 to 15.5 Mg ha-1, with linear response to nitrogen rates. The variable rate of nitrogen increased by 11.8 and 32.6% the nitrogen uptake and nitrogen use efficiency, respectively, compared to the uniform rate of nitrogen. However, no significant increase in grain yield was observed, indicating that the major benefit of the variable rate of nitrogen was reducing the risk of environmental impact of fertilizer.

Incidence rate and spatio-temporal clustering of type 1 diabetes in Santiago, Chile, from 1997 to 1998

OBJECTIVE: To estimate the incidence rate of type 1 diabetes in the urban area of Santiago, Chile, from March 21, 1997 to March 20, 1998, and to assess the spatio-temporal clustering of cases during that period. METHODS: All sixty-one incident cases were located temporally (day of diagnosis) and spatially (place of residence) in the area of study. Knox's method was used to assess spatio-temporal clustering of incident cases. RESULTS: The overall incidence rate of type 1 diabetes was 4.11 cases per 100,000 children aged less than 15 years per year (95% confidence interval: 3.06--5.14). The incidence rate seems to have increased since the last estimate of the incidence calculated for the years 1986--1992 in the metropolitan region of Santiago. Different combinations of space-time intervals have been evaluated to assess spatio-temporal clustering. The smallest p-value was found for the combination of critical distances of 750 meters and 60 days (uncorrected p-value = 0.048). CONCLUSIONS: Although these are preliminary results regarding space-time clustering in Santiago, exploratory analysis of the data method would suggest a possible aggregation of incident cases in space-time coordinates.

Effects of acupressure on progress of labor and cesarean section rate: randomized clinical trial

OBJECTIVE To analyze the effects of acupressure at the SP6 point on labor duration and cesarean section rates in parturients served in a public maternity hospital.METHODS This controlled, randomized, double-blind, pragmatic clinical trial involved 156 participants with gestational age ≥ 37 weeks, cervical dilation ≥ 4 cm, and ≥ 2 contractions in 10 min. The women were randomly divided into an acupressure, placebo, or control group at a university hospital in an inland city in the state of Sao Paulo, Brazil, in 2013. Acupressure was applied to the SP6 point during contractions for 20 min.RESULTS The average labor duration was significantly different between the SP6 acupressure group [221.5 min (SD = 162.4)] versus placebo [397.9 min (SD = 265.6)] and versus control [381.9 min (SD = 358.3)] (p = 0.0047); however, the groups were similar regarding the cesarean section rates (p = 0.2526) and Apgar scores in the first minute (p = 0.9542) and the fifth minute (p = 0.7218) of life of the neonate.CONCLUSIONS The SP6 acupressure point proved to be a complementary measure to induce labor and may shorten the labor duration without causing adverse effects to the mother or the newborn. However, it did not affect the cesarean section rate.